Between the optical frequencies and the microwave frequencies is a broad expanse of spectrum in the terahertz range. However, development of devices for operation in the terahertz range is hampered, to some extent, by a dearth of devices for manipulating or detecting terahertz waves.
Terahertz radiation is useful for a variety of purposes, including security systems. Because of its ability to penetrate most clothing, terahertz radiation provides a way to detect concealed weapons. Another use for terahertz radiation arises in the context of cancer treatment. Because of its ability to detect differences in water content and density of tissue, terahertz radiation can be used to reliably distinguish between normal cells and cancerous cells.
Electromagnetic metamaterials for supporting propagation of a particular wavelength consist of composites having a patterned metallic structure having dimensions on the order of the wavelength to be propagated. The interaction of these metallic structures with the surrounding medium results in a wave propagation medium that can have negative values of permittivity and/or permeability.